Hello all. Having only just registered with the forum I’m unsure if this subject has previously been raised. If so could you please direct me to the appropriate link. Could somebody please tell me if there is any link between raised co2 levels and aggression in a normally docile aquarium. I’m asking because after many months of trial and error I finally have a flourishing, planted, freshwater aquarium, thanks partly to a diy co2 infusion which I set up about 8 weeks ago. Unfortunately about 4 weeks ago I started to notice a male swordtail being unusually aggressive towards the 3 platy’s and more recently towards 6 zebra danio’s resulting in them all spending much of their time in hiding. I have considered territorial/mating behaviour but why now after 8 months of apparent harmony? Any information will be greatly appreciated. Many thanks.

Hi John 1.5″ is pretty small for a male sword but I wouldn’t be surprised that it hasn’t grown the way some of these domesticated forms have become. Maybe it’s just coming into sexual maturity hence the heightened aggression? To answer your original question I’ve never heard of CO2 added to aid plant growth affecting the behaviour of a fish before.

Hi John 1.5″ is pretty small for a male sword but I wouldn’t be surprised that it hasn’t grown the way some of these domesticated forms have become. Maybe it’s just coming into sexual maturity hence the heightened aggression? To answer your original question I’ve never heard of CO2 added to aid plant growth affecting the behaviour of a fish before.

Many thanks for the info Matt. Just one more query. As his behaviour is causing many of the other inhabitants to hide away for the majority of the time, would isolating him for a short period be of any help or should I just allow nature to take its own course?.

I don’t think the problem fish will learn to associate being isolated with bad behaviour. I’d actually lean the other way and suggest that it would be worse on returning to the tank as it then seeks to re-establish itself.

Many thanks to all for the info’ and comments. I’ll allow the culprit to strut his stuff for the time being. I’m hoping it doesn’t last too long as it’s a shame his “tankmates” don’t have the freedom to swim where they like at the moment. Ah well, Que Sera Sera.